All-optical transport offers significant advantages to carrier networks, including protocol and format independence and substantial cost savings from reduced numbers of OEO interfaces. However, routing in large-scale transparent networks, which may include many transparent network elements and/or long distances is problematic because of optical signal impairment accumulation along end-to-end routes. OEO conversion repairs these impairments but is expensive. In networks with transparent elements, especially large ones, it is difficult to locate OEO resources and then configure the network to use them efficiently. To support networks with transparent elements, operations support systems must assure design of networks with impairment-feasible routes (also referred to as “feasible routes”) and must be able to identify such feasible routes at the time of capacity activation.
A basic paradigm for network design and capacity activation in opaque networks, where OEO conversion occurs at each node, is illustrated in FIG. 1. This approach utilizes a Capacity Placement module that determines where to place equipment and capacity and how much to place. The input to the Capacity Placement module includes a network topology and a demand forecast, while the output is a high-level network design. Opaque networks are engineered link-by-link with OEO conversion at the nodes, ensuring that impairments do not accumulate across multiple links. Transparent network designs, however, must consider the effect of impairment accumulation across multiple links. FIG. 2 illustrates a possible updated approach for design and capacity activation in networks with transparent elements as more fully described below.
There are several known methods that apply constraints to limit impairments in an effort to assure the existence of impairment-feasible paths in optical network design. For example, Doshi et al, “Generic optimizations for transparent optical networks: the lightpath intelligent instantiator LIPI”; Technical Proceedings of the National Fiber Optic Engineer's Conference, pp. 47-55, Sep. 15-19, 2002, describes a method for modeling impairment along optical routes using a single distance-oriented metric and which locates regeneration along pre-selected routes. Farahmand et al “Characterization and representation of impairments for routing and path control in all-optical networks”; Technical Proceedings of the National Fiber Optic Engineer's Conference, pp. 279-289, Sep. 15-19, 2002, also discusses constraint mechanisms for limiting impairments along a path in a network with transparent elements. Further, Van Parys et al “Evolution towards transparent optical networks using selective wavelength regeneration and conversion”; Technical Proceedings of the National Fiber Optic Engineer's Conference, pp. 1012-1017, Jul. 8-12, 2001, describes a method wherein a distance constraint is imposed to limit the impairment along a transparent subpath. Similar constraints and a routing algorithm that constrains distance are also presented in Shen et al, “Sparse placement of electronic switching nodes for low blocking in translucent optical networks,” Journal of Optical Networking 1, 424-441 (2002). However, the routing algorithm presented in Shen et al may fail to identify feasible paths that exist in the network. The routing method presented in Yang and Ramamurthy, “Dynamic routing in translucent WDM optical networks,” Proceedings of IEEE ICC 2002, New York, N.Y., (2002) can also fail to identify existing feasible paths.
In general, the known methods for locating OEO capability operate by iteratively improving previously computed routes until they become feasible. Such methods could be used to assure feasibility between each pair of nodes by generating a path between each pair of nodes and then placing OEOs, as needed, along these paths to make them feasible. However, this typically results in placing more OEOs than are needed to assure the desired feasibility for the network. Methods of this type are presented, for example, in Shen et al and in Yang and Ramamurthy, “Sparse regeneration in a translucent WDM optical network,” Proceedings of the Asia Pacific Optical and Wireless Communications Conference (APOC), C. Qiao and S. Xie, (eds.), Proc. SPIE 4585, (2001).
As further shown in FIG. 1, once the network is constructed, a separate operations support system typically handles capacity provisioning for setting up connections on request. The inputs to such a system are a network design (for example, a network design generated by the Capacity Placement module) and a sequence of client connection requests. The output is either a route and wavelength assignment for each request or a notification that the connection cannot be satisfied.
There remains a need in the art for improvements in the technology of design and routing of optical networks that contain transparent elements.